The present invention relates generally to propellant transferring systems for use with spacecraft propulsion systems, and more particularly, to an integrated storage and transfer system and method for storing and transferring propellant to a spacecraft for use by a spacecraft propulsion system.
The assignee of the present invention manufactures and launches spacecraft that use onboard thrusters to orient and reposition the spacecraft while it is in orbit to optimize its location and orientation. Two part propellent, or bipropellant as it is known, comprising fuel (hydrazine) and oxidizer (N.sub.2 O.sub.4), is loaded into separate storage tanks on the spacecraft prior to launch. In operation, the two bipropellant liquid propellants are combined in a plenum under computer control to cause operation of selected thrusters to achieve proper spacecraft orientation.
In the past, an elaborate procedure has been used to obtain, transport and load the bipropellant liquid propellants into the spacecraft. This procedure is time consuming, costly, and poses many unnecessary environmental and safety risks. This procedure is described with reference to FIG. 1 of the drawings. More specifically, FIG. 1 shows a procedural flow diagram illustrating a conventional procedure (10) for acquiring, shipping, and loading bipropellant liquid propellants into a spacecraft. Suppliers of the hydrazine and oxidizer liquid propellants independently fill (11, 12), as required, enough fifty-five gallon drums of fuel and small oxidizer containers of the respective propellants to fill an order. The fifty-five gallon drums and small containers are used because of Department of Transportation requirements for transporting the highly toxic and hazardous bipropellant materials to the spacecraft launch site. The loaded fifty-five gallon drums of fuel and small containers of oxidizer along with fuel and oxidizer servicing carts are shipped (13) to the launch site.
At the launch site, the fuel cart and fifty-five gallon fuel drums are set up and prepared (14) for fuel transfer. Similarly, the oxidizer cart and the small oxidizer containers are set up and prepared (15) for oxidizer (N.sub.2 O.sub.4) transfer. A molecular sieve is prepared 16 that is used during cart service to remove iron (Fe) from the N.sub.2 O.sub.4 oxidizer. This has heretofore typically occurred during all propellant loading operations. Fuel is then transferred (17) from the fuel drums into a fuel service cart. Oxidizer is then transferred (18) from the small containers into an oxidizer service cart. These two steps are repeated to transfer the fuel and oxidizer from each require fuel and oxidizer container into the respective fuel and oxidizer service carts. After the fuel and oxidizer is fully transferred to the respective fuel and oxidizer service carts, each respective cart is sampled (19, 21) to determine if there is any contamination of either of the liquid propellants due to the transfer. Thereafter the propellants are conditioned 22 for a period of five days. This conditioning operation ensures that the temperature of the propellants are substantially the same as that of the spacecraft, and provides for helium saturation of the fuel and oxidizer. Thereafter, the respective fuel and oxidizer service carts are further pressurized (23) using helium to force the fuel or oxidizer out of its respective cart and into the respective storage tanks in the spacecraft. The loading equipment, molecular sieve and carts are then cleaned (24) per Department of Transportation requirements for hazardous materials shipment. The fuel and oxidizer drums are then cleaned (26)and returned to the respective supplier or disposed of, as the case may be. The oxidizer propellant container is returned (26) to the supplier for refill and reuse.
As should be clear from the above description, this procedure (10) is complicated and time-consuming creates environmental hazards, and potentially exposes support personnel to injury. The procedure takes approximately thirty-five days to complete for a typical spacecraft. This long time period and the required sampling has contributed greatly to the costs of loading propellant into the storage tanks in the spacecraft.
Accordingly, it is an objective of the present invention to provide for a system and method that improves upon this conventional procedure and provides a highly efficient, cost-effective and environmentally safe means for obtaining, transporting, and loading the constituent propellants into a spacecraft.